X-Message-Number: 26057
Date: Tue, 19 Apr 2005 09:27:49 -0400
From: Thomas Donaldson <>
Subject: To Daniel Crevier, again:

For Daniel Crevier, again:

If you read my comments again you will note that I am not arguing against
digital computers at all. I am arguing against the possibility of making
a brain simulation using time-sharing, a quite different problem. And if
we take our time-sharing brain simulation into the real world, it will
fail, no doubt with a delay (which I personally suspect won't be very
long) depending on just how parallel the brain simulation is. And of
course for a computer to be a parallel computer, you require physically
separate computers working simultaneously. A simulated parallel computer
just doesn't do that.

If, however, we start thinking about many analog computers all working
in parallel, you do start to get something. You'll need a lot more,
but if we form our memories from the way in which are neurons are 
connected then analog computers (imitating in analog the workings of
neurons) might actually be designed to do exactly that. A big step, 
but not the whole distance, towards a real conscious computer-brain.
It looks much easier to make analog devices (even from living cells)
able to grow dendrites and axons, and new synapses, and even able to
produce new neurons, than we could from any digital device.

And if we try to implement not only a brain, but a person in a simulated
computer world, we get into lots of problems, as Bob Ettinger has 
briefly discussed and as I described in my last message to you.

Incidentally, the problem with predicting the weather is deeper than 
our choice of algorithms and computers to do so. By its nature, the
weather is unstable. Small variations in a solution blow up with
time. This is not a problem solvable by either digital or analog
computers except (as I said) for a finite future time span, and the
calculations can only do that if they're far more accurate than 
the final result during that time. Of course, no matter how accurate
you make your calculations, with time your solution will cease to
be accurate at all.
            Best wishes and long long life for all,

                Thomas Donaldson

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